Presentation spotlightUnderstanding the pitfalls of glaucoma surgery

Despite huge improvements in glaucoma surgery techniques and management and the development of new technologies, glaucoma surgeons still face major issues with filtration surgery with regard to poor visual outcomes and bleb fibrosis. The failure of filtration surgery is the main limitation of glaucoma surgery.
“The common point of antiglaucoma filtering surgery is the filtering bleb,” said Amel Ouertani, MD, Centre Alhakim, El Khadra, Tunis, Tunisia, in a presentation she gave on the topic at the 2018 World Ophthalmology Congress. “Blebs are dynamic and evolve over time and must be monitored. The success of surgery often depends on appropriate and timely postoperative intervention to influence their functioning.”

Bleb appearance

Dr. Ouertani carefully examines external aspects of the filtering bleb: size, diffuse or localized aspect, height, bleb wall thickness, inflammation, and vascularization. A good, functional bleb forms during the first week after surgery. It should be diffuse and will tend to become localized at 2–3 weeks after surgery, without defined limits. Blebs are slightly opalescent with epithelial microcysts. The final aspect is acquired at approximately 3 months postoperatively.
“Early detection of filtering bleb failure is associated with the identification of a progressive and irreversible increase in IOP during the first 2 to 4 weeks after surgery,” Dr. Ouertani said. “Other signs are the presence of blood inside or surrounding the bleb, the development of Tenon’s cyst, and a progressive flattening of the bleb.”

Filtering bleb complications: Hypotony

Bleb complications are associated with either hypotony, hypertony, or normotony. The most common cause of hypotony is leakage, which can be early in onset, occurring usually within the first 3 months after filtration surgery. Leakage results from a non-watertight bleb, which can arise as a result of surgical trauma, conjunctival perforations, non-watertight sutures, a loose scleral flap, or from antifibrotics. Late-onset leakage occurs after 3 months from surgery and is usually associated with the intra- or postoperative use of antifibrotics. Symptoms include a thin ischemic bleb, low IOP, Seidel positive, and what appears as tearing.
“If not treated, the clinician will encounter further complications that are associated with hypotony like a shallow AC, goniosynechiae, and cataract. There can be corneal decompensation, choroidal detachment, choroidal effusion, hypotensive maculopathy, and an increased risk of infection,” she said.
Prevention includes minimizing surgical trauma, careful closure of the scleral flap, watertight conjunctival closure (paracentesis), and the careful use of antifibrotics. Treatment for early onset leakage depends on whether antifibrotics were used. If not, spontaneous healing is possible if the leak is small. If the leak is more important, conservative therapy is the first option, using carbonic anhydrase inhibitors and antibiotics and reducing corticosteroids, with a compression patch. If the leak is larger and there is a perforation, biological glue and a therapeutic lens can be used. If the bleb is flat and the AC shallow, surgical closure is required. Treatment of late-onset leakage can still be conservative, but other indications are usually necessary, such as an autologue venous blood injection into the bleb to induce fibrosis, or surgical, involving sutures. If the flap looks necrotic, conjunctival or scleral grafts or amniotic membrane grafts may be useful.
Other causes of hypotony are over filtering and infection. The treatment for over filtering blebs includes lubricants and NSAIDs for discomfort. If hypotony is persistent, a compressive suture, cryotherapy, or argon laser treatment to induce fibrosis and reduce filtration are options. Infection is a rare cause of hypotony. Risk factors include antifibrotics, leakage, limbus-based conjunctival flaps, an inferior surgical site, and young patient age. Prevention involves cautious antifibrotic use, effective leakage treatment, and the avoidance of bleb procedures in young patients. Infections are treated with antibiotics and corneal patching when involving necrotizing blebitis.

Filtering bleb complications: Hypertony

A hypertonic filtering bleb can result from tight sutures, internal obstruction, or conjunctival fibrosis. “If the closure is too tight, you can prevent it by using adjustable sutures and treat with argon laser suture lysis,” Dr. Ouertani said. “Obstruction of the filtering site can be caused by the iris, vitreous, ciliary body, lens, or from blood. Prevention is a large base iridectomy and treatment is with argon laser for pigmented sutures and Nd:YAG laser for non-pigmented sutures. The main complication of filtering surgery is conjunctival fibrosis. Success of the surgery depends on the incomplete scarring of the surgical wound.”
Fibroblastic proliferation begins on the fifth or sixth day after surgery and continues for around 1 year. A vascularized and thick-walled bleb is likely to be fibrotic. A fibrotic bleb is shallow and sometimes encapsulated. Preventing bleb fibrosis at the preoperative stage includes treatment of the ocular surface and adnexa with anti-inflammatory medication and cessation of preserved anti-glaucoma drops 1 month before surgery. Perioperatively, Dr. Ouertani advised the careful choice of the trabeculectomy site, the avoidance of scars, and the protection of the conjunctival flap. “We have to be gentle with hemostasis because vascular aggression will cause fibrin clots and platelet activation, which activate inflammatory mediators, like VEGF, cytokines, and interleukins, causing a severe fibrotic reaction,” she said.

Fibrosis

“Evidence suggests that intraoperative MMC is more effective than postoperatively administered 5-FU, particularly in patients at high risk of surgical failure,” Dr. Ouertani said. “Other evidence showed no difference in primary trabeculectomy eyes that were followed long term when both agents were used intraoperatively. Overall, MMC is considered to be more effective at long-term reduction in IOP and in cases of refractory glaucoma.”
According to the European Glaucoma Society, indications/protocol for MMC are tailored to the severity of glaucoma: for medium risk glaucoma, give 5-FU or MMC and for high-risk glaucoma, give MMC, using the conventional soaked sponge method or by sub-Tenon’s injection.
Antifibrotic complications include corneal ulceration, scleral necrosis, conjunctival perforation, thin-walled and ischemic blebs, and chronic hypotony. Anti-VEGF agents are indicated as they have a direct effect on vascular proliferation and an indirect effect of reducing the influx cytokines into the bleb. But there is no consensus about their efficacy especially in refractory glaucoma.
“Anti-inflammatory agents are crucial after surgery. A long course of corticosteroids and NSAIDs should be planned according to the bleb status. Corticosteroid injections with dexamethasone have been shown to reduce fibrosis and improve bleb status. In vitro diclofenac and phenidone have been shown to reduce fibrosis proliferation and cell attachment. New adjuvants capable of specifically modulating conjunctival wound healing without the associated side effects are under study,” she said.
Early fibrosis is treated with pressure and laser suture lysis. In late-stage fibrosis, needling is a safe and effective method to save a failed or failing filtering bleb. The principle is to disrupt subconjunctival scar tissue, usually followed by the injection of 5-FU or MMC. Blebs that are needled within the first 3 months of filtration surgery have a better prognosis than after 3 months, after which trabeculectomies all have the same prognosis. While there is no real consensus, Dr. Ouertani thinks that multiple needlings and high IOP immediately after needling have poor prognoses. Several failed needlings are an indication for a new surgery.

Editors’ note: Dr. Ouertani has no financial interests related to her comments.